Method of forming and dressing grinding wheels



June 1 H948. w mw g -rr 2,442,627

METHOD OF FORMING AND DRESSING GRINDING WHEELS Filed July 13, 1943 2 Sheets-Sheet 1 June 1948. J. E. WAINWRIGHT 2,442,627

METHOD OF FORMING AND DRESSING GRINDING WHEELS Filed July 13, 1943 2 Sheets-Sheet 2 jrvenior Patented June 1, 1948 2,442,627 METHOD OF FORMING AND DRESSING BINDING WHEELS John Ernest Wainwright, Hunningliam, near Leamington Spa, England, assignor to Coventry Gauge & Tool Company Limited, Coventry,

England In Great Britain August 6, 1942 Application July 13, 1943, Serial No. 494,518

1 Claim. 1

This invention relates to the forming and dressing of grinding wheels employed in form-grindin operations, such as are used in the production and/or finishing of screw threads, and more particularly but not exclusively to grinding wheels of the multi-rib type in which the form is produced by a method of generation.

The orthodox method of generation involves the use of a tool which, particularly when required for use in dressing or forming multi-ribbed wheels for producing screw threads of fine pitch, is not only itself difllcult to produce but is attended by a considerable liability to failure when in service owing largely to its unavoidably inherent mechanical weakness. Usually, the grinding wheel is first roughed out to form a series of serrations having a pitch which is a multiple of that of the screw thread to be produced and-a depth somewhat in excess of that of the said thread. The finishing operation is then performed by means of a cone tool suitably radiused and operated by means of a cam of the actual pitchrequired, the tool being operative on the wheel during alternate cycles only.

The object of the present invention is to provide a. method of producing the required threadform on the wheel which not only enables a dressing tool of a much more robust form to be used but also allows for the maximum tolerance in the manufacture of. the tool and a certain amount of compensation for wear.

In the method of forming and dressing grinding wheels according to this invention the required form is produced in stages, one part of the form being produced in its true form and position in one stage and the other part finished in another stage.

After completion of the first stage of the forming operation and before commencing the second stage, the relationship between the wheel and the forming tool is changed in such a manner that when during the second stage the tool is again traversed across the wheel, the second part of the form is produced in its correct relationship with the first part.

In order that the invention may be clearly understood and readily carried into practical efiect. reference is made in describing the same to the accompanying drawings which illustrate, by way of example, the application of the invention in forming a multi-ribbed grinding wheel for use in producing screw threads.

Figure 1 is an enlarged view of the preferred form or cutting tool.

Figure 2 is a graphic representation on an exaggerated scale of the first stage of the improved method of forming the wheel.

Figure 3 is a similar representation of the second stage.

Figure 4 shows a preferred type or cam.

Figures 5 and 6 illustrate tools having oblique or inclined noses.

Figure 7 is a plan view of a machine for use in carrying out the improved wheel forming operation.

Figure 8 is a detail view on a larger scale of the lead screw and rotatable nut mechanism.

Figure 9 is a detail cross-sectional view of the mechanism for rotating the nut of the lead screw for side out purposes.

In forming the peripheral surface of a grinding wheel for use more particularly in producing screw threads of fine pitchby a grinding operation, the wheel surface is first formed by a plunge cut roughing operation in the known manner with a series of annular serrations of substantially V-form in cross-section and having a pitch which is a multiple of that required on the work piece.

The method of finishing these serrations to the required screw thread form according to this invention allows of the use of a tool of a form which is more robust than can at present be employed and one that will permit of the maximum tolerance in the manufacture of the tool and which will permit of some compensation for wear. For this purpose the tool 2, which may be a diamond or made of any other appropriately hard material is of preferably prismatic form of V-section with a fiat nose "2. as shown in Figure 1.

The improved method involves the use of a cam or former which whilst containing all the necessary component parts of the final form required on the grinding wheel, also permits of adjustments for wear and inaccuracy of the forming tool by means ofordinary indexed controls incorporated in the machine employed for the wheel-forming operation, the arrangement being such that although the tool may be of unsymmetrical form or not of consistent dimensional accuracy, it may yet produce symmetrical and accurate form's'to a, major degree.

Where a cam is employed its speed of rotation will be co-related with the speed of traverse of the tool. The improved method also involves the provision of means for imparting an in-feed and/or side cut during or preceding the second stage of the wheel-forming operation.

The path and direction of movement of the tool 2 during the first stage of the wheel-formin operation is indicated in Figure 2 by the chain dotted line. In the arrangement shown this path is produced by the cam 3 shown in Figure 4 and in considering the action of this cam on the tool it must be remembered that during the forming operation the tool is being traversed or moved to the right axially of the wheel at the same time at a constant speed across the face of the grinding wheel 4 as indicated by arrows in Figures 2 and 3,

either by the usual lead screw or by any other appropriate mechanism.

The profile of the cam and its speed of rotation relatively to the traversing motion of the tool is such that one complete revolution of the cam is equivalent to one pitch of the form to be produced on the wheel. I

The ordinates A to I in Figure 2 show the position of the tool 2 for each correspondingly marked part of the profile of the cam 3 during the first stage of the operation.

Assuming the cam to be rotating in the direction of the arrow in Figure 4 and the direction of traverse of the tool being to the right as indicated by the arrow in Figure 2, and assuming the tool to have completed the left flank I of the form to its true shape as far as the crest i. e. to the ordinate A, the concentric portion of the cam allows the tool to move sub stantially parallel with the axis of the wheel I for a short distance from A to B. The next part of the cam profile b-c causes a withdrawal of the tool in an oblique direction from B to C. This withdrawal enables the tool to clear the crest t of the form in the event of any inaccuracy in the tool due to wear or to the nose of the tool being slightly convex. With a tool inwhich the nose is perfectly flat and truly at right angles to the axis of the tool no withdrawal of the latter from B to 0 would be necessary, the cam in this case being formed to cause the tool to move forward from the one flank to the other at the same time the grinding wheel is infed or moved radially of its axis towards the tool 7 an amount suillcient to remove the excess mawith the nose tangential to the crest of the form.

This, of course, would involve th having a long dwell from a to e. 4

Since, however, it is not practical to obtain a tool which is not only perfect but which will not wear, it is advisable to provide the cam with withdrawal and infeed steps b-c and 11-h respectively. During the rotation of the cam from c to d the tool is caused to follow a straight path to the right and inclined from left to right from C to D radially inwardly or the wheel 4 followed by a short parallel movement to the right from D to E which is allowed by the concentric portion de of the cam-profile. The next portion e/ of the cam profile causes the tool to move from E to F to form the other flank of the form, after which the tool is again allowed to move forward to the right a short distance from F to G by the concentric part j-o of the cam profile. The tool is then moved inwardly in an oblique direction from G to H by the portion 9-); of the cam after which it is, allowed to move forward to the right in a parallel direction from H to I, by the concentric portion h-i of the cam. The remaining part of the cam profile from i to a is responsible for the movement of the tool from I to A in forming the flank of the next form to its true shape.

It will be seen that in passing from one flank of the form to the other and from one cutting edge to the other, the tool is in effect off-set in a forward direction or to the right and to an extent determined by the portion of the cam AE so that the form produced at the end of the first stage of the operation is' thicker than is required, as indicated by the cross-hatched portion in Figure 2. This excess material is removed during the second stage of the forming operation. v

Before commencing the second operation the position of the tool in relation to the wheel is changed, the tool being ofi-set in a rearward direction or to-the left to give a side-cut, and

euseofacam terial left on the second or right-hand flank I of the-form. This position of the tool is shown in Figure 3 where it will be seen that in moving from I to A the tool 2 under the influence of the portion ta of the cam, is clear of the left flank I of the form. After moving forward a short distance from A to B and being withdrawn from B to C by the corresponding portions 0-1: and b-c of the cam, the tool, in passing from C to D, is caused by the portion o-d of the cam to take up the cut in a direction at a tangent to the crest 6 of the form and after a short parallel movement to the right from D to E, alhiwed by the dwell de on the cam, the tool in moving from E to F removes the excess material left on the right hand flank 'I of the form in the first stage of the operation. The tool is then allowed to move to the right parallel to the axis of the wheel 4 a short distance from F to G by the dwell f-g on the cam, after which it is moved radially inwardly of the wheel 4 from G to H by the stepg-Jt on the earn, the cycle being completed by the parallel movement from H to I allowed by the concentric portion hi of the cam.

In actual practice, as shown in Figure 3, the amount the tool is withdrawn from B to C is greater than is necessary to provide for ordinary inaccuracies and wear of the tool, and greater than the amount the tool is moved inwardly from G to H. This difl'erence is to avoid the full passage of the nose flat of the tool across the crest of the wheel. An infeed of an appropriate amount, is given by moving the wheel towards the tool to the extent required to give the correct depth to the finished form. The amount of this infeed will vary according as to which of the two edges of the tool is nearer to the wheel. For example, if the nose of the tool 2 is oblique in the direction shown in Figure 5 so that the leading edge 8 is nearer to the wheel than the following edge I, the distance 0 must not exceed the in-feed allowance and must be added to it. If, however, theobliquity is in the opposite direction, as seen in Figure 6, the distance 0 must likewise not exceed the infeed allowance and in this case must be subtracted from it.

' The improved method above described may be carried out by means of a machine of substantially the construction shown in Figure 7 in which provision is made for controlling the'side-cut and in-feed factors.

In the construction shown, the grinding wheel 4 to be formed, together with its driving motor II, is carried by a slide I 2 which is movable for infeed purposes along a stationary bed It by means of a screw ll Journalled in the latter and engaging a nut It on the slide, The said screw, which is prevented from axial movement in any suitable manner, has a calibrated head It and is operated by a handle II.

The tool 2, which operates on the grinding wheel, is slidably mounted in a casing ll supported between the centres It of a work-head 2| and tailstock 2i both of which are carried by a table 22 free to reciprocate upon the bed 22 of the machine. 4

The movement of the tool in a direction towards and away from the axis of the grinding wheel, that is to say, the depth component of the form-generating motion is derived from the cam I which is enclosed within the said casing ll.

The cam is rotated at the appropriate speed relatively to the traverse of the table 22 by means of gears 26, 21 also enclosed within said casing. Gear 21 is arranged with its axis coincident with the axis of the aforesaid centres l9 and is driven from the rotating face plate 28 of the workhead 29 by means of a driving pe 29 engaging an arm 30 on the spindle of the said gear 21. The face plate is itself carried and driven by the work-head spindle in the usual way.

The reciprocatory motion, or traverse, of the table 22, and hence of the tool, that is to say, the pitch component of the form-generating motion, is derived from a lead screw 3! journalled in the bed 23 of the machine and engaging a nut 32 carried by a lug 33 on the underside of the table, as shown in Figure 7 and more clearly in Figures 8 and 9. The lead screw is driven from a splined shaft 34 through gearing in the usual manner.

For the purposes of enabling the tool to be oil-set or moved to the left to give the necessary side-cut during the second stage, the nut 32, instead of being fixed in the lug 33 on the table, is rotatably mounted therein and provided at one end with a helical gear wheel 35 which is in constant mesh with a similar wheel 36 fixed to a shaft 31 journalled in the table 22. This shaft is provided at the front of the machine with a calibrated hand wheel 38. By rotating this shaft in one direction the nut 32 is rotated relatively to the lead screw 3|, thereby temporarily decelcrating the normal traversing speed of the table and hence of the pitch component motion of the tool to give a side-cut.

While I have used the terms right and left herein to identify the flanks of the serrations of the wheel 4 and the direction of the traverse feed movement and the direction of advance or retardation or oil-sets of the tool, it is to be understood such expressions are merely for purposes of illustration or explanation and that the embodiment might be such that such directions would be reversed; also that the wheel might be moved instead of the tool to give the desired relationship between the wheel and tool or vice versa, and such references to movement of the wheel and tool and to the direction of such movement by the expressions as used in the specification and claims are used in that general sense, it suificing if the desired or necessary'relationship between the wheel and tool during the various phases of the cycles and stages of operation is attained whether attained by movement of the tool or wheel or both.

Although the invention is more particularly intended for use in forming wheels for use in the production of screw threads, it will be obvious that the same method can be applied in the production of other form I claim:

A method of forming or dressing the serrated face or form-grinding wheels by a single dressing tool in a two-phase multi-cycle two stage forming or dressing operation, said method consisting of the following steps; first, rotating the wheel and causing the tool to move intimed relation thereto throughrepeated cycles of operation while traversing the tool across the face of the wheel and repeating the traverses of the tool to the right across the face of the wheel until completion of the first stage of operation wherein the left flanks and left portion or the crests oi the serrations are trued to finished form by the first phase of the cycles of operation and the right crest portions and flanks of the serrations and the intervening valleys are dressed by the second phase of said cycles of operation of the first stage to semi-finished form; secondly, causing relative movement between the wheel and tool to position the tool to the left beyond the extreme left serration a sufiicient distance to remove the thickness of material to be removed successively from the right crest portion and right fiank of each serration and to position the tool radially inwardly of the wheel a distance equal to the thickness in a radial direction of the material to be removed from the right portion of the crest of each serration; thirdly, rotating the wheel and causing the tool to move in timed relation thereto through repeated cycles of operation while traversing the tool to the right across the face of the wheel and repeating the traverses to the right of the tool across the wheel until completion of the second and final stage of operation wherein the remaining portions of the crests and the right flanks of the serrations and faces of the intervening valleys of the wheel are formed or dressed to true finished form; each cycle of operation of the first stage comprising a radially outward first phase of movement of the tool with its leading side edge in engagement successively with the left fiank and crest of a serration, a superimposed radially outward movement of the tool followed by movementthereof axially of the wheel to the right after completion of the first phase and with the tool out of contact with the wheel before commencement of the second phase, a radially inward second phase of movement of the tool toward the wheel with its end edge and trailing side edge successively in engagement with the periphery and right flank of said serration and finally with the end edge and leading side edge successively of the tool in engagement with the face of the adjacent valley; and each cycle of operation of the second stage involving the same movements of the tool, only with the first phase starting with the end edge and leading side edge of the tool in engagement with the right portion of the serration succeeded by the engagement of the end edge and left and trailing side edge of the tool with the right flank of such serration and by engagement of the end edge and leading side edge of the tool with the face of the adjacent valley to the right, and finally by the tool moving radially outward of the wheel in a movement corresponding to the movement of the first phase of the cycles of the first stage but throughout such final movement out of contact with the wheel.

JOHN ERNEST WAINRIGHT.

REFERENCES CITED The following references are of record in the file of this patent: V

UNITED STATES PATENTS Number Name Date 1,594,393 Vokel Aug. 3, 1926 1,764,043 Hanson June 17, 1930 2,176,350 Locke Oct. 17, 1939 2,213,665 Brendel et al. Sept. 3, 1940 2,237,977 Wainwright Apr. 8, 1941 2,292,947 Kasparson et al. Aug. 11, 1942 FOREIGN PATENTS Number Country Date 525,932 Great Britain Sept. 6, 1940 

